Naturally occurring and synthetic estrogens have broad therapeutic utility, including: relief of menopausal symptoms, treatment of acne, treatment of dysmenorrhea and dysfunctional uterine bleeding, treatment of osteoporosis, treatment of hirsutism, treatment of prostatic cancer, treatment of hot flashes and prevention of cardiovascular disease. Because estrogen is very therapeutically valuable, there has been great interest in discovering compounds that mimic estrogen-like behavior in estrogen responsive tissues.
For example, estrogen-like compounds would be beneficial in the treatment and prevention of bone loss. Bone loss occurs in a wide range of subjects, including women that are post-menopausal or have had a hysterectomy, patients who were or are currently being treated with corticosteroids, and patients having gonadal dysgenesis. The current major bone diseases of public concern are osteoporosis, hypercalcemia of malignancy, osteopenia due to bone metastases, periodontal disease, hyperparathyroidism, periarticular erosions in rheumatoid arthritis, Paget's disease, immobilization-induced osteopenia, and glucocorticoid-induced osteoporosis. All of these conditions are characterized by bone loss, resulting from an imbalance between bone resorption, i.e. breakdown, and bone formation, which continues throughout life at the rate of about 14% per year on the average. However, the rate of bone turnover differs from site to site, for example, it is higher in the trabecular bone of the vertebrae and the alveolar bone in the jaws than in the cortices of the long bones. The potential for bone loss is directly related to turnover and can amount to over 5% per year in vertebrae immediately following menopause, a condition which leads to increased fracture risk.
In the U.S., there are currently about 20 million people with detectable fractures of the vertebrae due to osteoporosis. In addition, there are about 250,000 hip fractures per year attributed to osteoporosis. This clinical situation is associated with a 12% mortality rate within the first two years, while 30% of the patients require nursing home care after the fracture.
Osteoporosis affects approximately 20 to 25 million post-menopausal women in the U.S. alone. It has been theorized that the rapid loss of bone mass in these women is due to the cessation of estrogen production of the ovaries. Since studies have shown that estrogen slows the reduction of bone mass due to osteoporosis, estrogen replacement therapy is a recognized treatment for post-menopausal osteoporosis.
In addition to bone mass, estrogen appears to have an effect on the biosynthesis of cholesterol and cardiovascular health. Statistically, the rate of occurrence of cardiovascular disease is roughly equal in postmenopausal women and men; however, premenopausal women have a much lower incidence of cardiovascular disease than men. Because postmenopausal women are estrogen deficient, it is believed that estrogen plays a beneficial role in preventing cardiovascular disease. The mechanism is not well understood, but evidence indicates that estrogen can upregulate the low density lipid (LDL) cholesterol receptors in the liver to remove excess cholesterol.
Postmenopausal women given estrogen replacement therapy experience a return of lipid levels to concentrations comparable to levels associated with the premenopausal state. Thus, estrogen replacement therapy could be an effective treatment for such disease. However, the side effects associated with long term estrogen use limit the use of this alternative.
Other disease states that affect postmenopausal women include estrogen-dependent breast cancer and uterine cancer. Anti-estrogen compounds, such as tamoxifen, have commonly been used as chemotherapy to treat breast cancer patients. Tamoxifen, a dual antagonist and agonist of estrogen receptors, is beneficial in treating estrogen-dependent breast cancer. However, treatment with tamoxifen is less than ideal because tamoxifen's agonist behavior enhances its unwanted estrogenic side effects. For example, tamoxifen and other compounds that agonize estrogen receptors tend to increase cancer cell production in the uterus. A better therapy for such cancers would be an anti-estrogen compound that has negligible or nonexistent agonist properties.
Although estrogen can be beneficial for treating pathologies such as bone loss, increased lipid levels, and cancer, long-term estrogen therapy has been implicated in a variety of disorders, including an increase in the risk of uterine and endometrial cancers. These and other side effects of estrogen replacement therapy are not acceptable to many women, thus limiting its use.
Alternative regimens, such as a combined progestogen and estrogen dose, have been suggested in an attempt to lessen the risk of cancer. However, such regimens cause the patient to experience withdrawal bleeding, which is unacceptable to many older women. Furthermore, combining estrogen with progestogen reduces the beneficial cholesterol-lowering effect of estrogen therapy. In addition, the long term effects of progestogen treatment are unknown.
In addition to post-menopausal women, men suffering from prostatic cancer can also benefit from anti-estrogen compounds. Prostatic cancer is often endocrine-sensitive; androgen stimulation fosters tumor growth, while androgen suppression retards tumor growth. The administration of estrogen is helpful in the treatment and control of prostatic cancer because estrogen administration lowers the level of gonadotropin and, consequently, androgen levels.
The estrogen receptor has been found to have two forms: ERα and ERβ. Ligands bind differently to these two forms, and each form has a different tissue specificity to binding ligands. Thus, it is possible to have compounds that are selective for ERα or ERβ, and therefore confer a degree of tissue specificity to a particular ligand.
What is needed in the art are compounds that can produce the same positive responses as estrogen replacement therapy without the negative side effects. Also needed are estrogen-like compounds that exert selective effects on different tissues of the body. Specifically, what is needed are compounds that exhibit a potent, selective affinity for ERα, and act as antagonists on breast and uterine tissues and as agonists on bone and lipids.
The compounds of the instant invention are ligands for estrogen receptors and as such may be useful for treatment or prevention of a variety of conditions related to estrogen functioning including: bone loss, bone fractures, osteoporosis, glucocorticoid induced osteoporosis, Paget's disease, abnormally increased bone turnover, periodontal disease, tooth loss, rheumatoid arthritis, osteoarthritis, periprosthetic osteolysis, osteogenesis imperfecta, metastatic bone disease, hypercalcemia of malignancy, and multiple myeloma, cartilage degeneration, endometriosis, uterine fibroid disease, cancer of the breast, uterus or prostate, hot flashes, cardiovascular disease, impairment of cognitive function, cerebral degenerative disorders, restenosis, gynecomastia, vascular smooth muscle cell proliferation, obesity and incontinence.